A human challenge-response test, sometimes referred to as a CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) can be used to verify whether a user who is attempting to access services through the internet is human or not. A CAPTCHA is an image of one or more words that are distorted or obscured in some way. By distorting or obscuring the words, it is less likely that an automated program (e.g., an internet robot) or a machine process (e.g., optical character recognition programs) would be able to recognize and decipher the words. A user is assumed to be human if the user is able to correctly enter the words that are displayed in a CAPTCHA.
A CAPTCHA verification process can involve at least four server calls from a user device. To access an online resource, the user device sends a first server call to a web page associated with the online resource. The web page then redirects the user device to send a second server call to a CAPTCHA server to retrieve a CAPTCHA image. The user device then sends a third server call to the CAPTCHA server with a solution to the CAPTCHA image. If the user's solution is correct, the user device is then redirected again to send a fourth server call to the original web page associated with the online resource.
The use of CAPTCHA on mobile devices has been limited because of the limited display resolution available on mobile devices. Solving the CAPTCHA by a human requires visual recognition of the words by the human eye, and the limited display resolution on mobile devices makes it difficult even for the human eye to decipher the CAPTCHA. Furthermore, as described above, the use of a CAPTCHA verification process requires at least four server calls from a user device. While this may be acceptable for conventional networks that have ample communication bandwidth available, the high number of server calls for a mobile device may significantly increase the amount of time it takes to complete the verification process due to the limited bandwidth of mobile networks.